A gas water heater generally provides a control pilot light for the main burner, a regulating device for the burner controlled by manual controls and by the temperature of the water and a safety device, which prevents the flowing of the gas to the burner in the case of turning off the pilot light.
Although water heaters with burners provided of piezoelectric or electronic type lighting devices are normally on sale, water heaters having flame lighting system for the gas burners are still commonly produced.
In a safety device for a gas water heater of known type, the cutoff shutter is downstream of the control shutter and upstream of a thermostatic shutter for the main burner. The control shutter is also controlled by a holding, electromagnet, in turn fed by the current of a thermocouple heated by the pilot flame. The thermostatic shutter is adjustable through a knob, which further provides a given start position, of minimum feed, for the gas burner.
In the condition of rest, the cutoff shutter is open and the control shutter is closed. When is depressed, the starting button closes the cutoff shutter and opens the control shutter. In this condition, the user can light the pilot light whilst, for the action of the thermocouple, the electromagnet holds open the control shutter. A following lifting of the button opens the cutoff shutter and allows the flow of the gas to the burner under the control of the thermostatic shutter and its automatic lighting by the pilot light.
The known safety device is generally effective to prevent the feeding of the main burner before the lighting of the pilot light, avoiding risks of saturation of the combustion chamber and consequent bursts. Nevertheless, the phase of starting of a lighting valve can be source of problems, particularly in the cases in which the user manually lit the pilot light by means of matches, lighters and free flames. A particular risk arises when the thermostatic shutter is open and the user unintentionally releases the starting button before moving away the hand from the area of the pilot light. A sudden lighting of the main burner during the return to rest of the button can cause fear and burns in the most unfavorable cases.
However, also if a water heater provides a piezoelectric or electronic system for the lighting of the pilot light, the safety device above described can cause problems. It may depend on improper sequences in the depression/lifting operations of the starting button and/or to anomalies in the functioning of the system, with hazards of leaks of gas in the combustion chamber and consequent hazards of bursts.